Conventionally, OTDRs inject a series of optical pulses into a fiber under test and extract, from the same end of the fiber, light that is scattered (i.e., Rayleigh backscatter) or reflected back from points along the fiber. Results from OTDRs are used for estimating the fiber's length, overall attenuation, and discontinuities along the fiber. Traditionally, OTDRs are external devices relative to optical network elements (e.g., WDM systems) which operate while the fiber under test is dark (i.e., no working traffic from the optical network elements). Thus, conventional OTDRs are not designed for integration with WDM systems or to operate in-service with such WDM systems. An embedded OTDR would allow a network operator to monitor the health of fiber plant in real-time as well as provide additional advanced applications. Also, conventional OTDRs are uni-directional meaning that OTDR pulses are launched from a downstream node of the fiber under test, but not from the upstream node. This makes it difficult to detect “events” such as pinched fibers, lossy connectors or splices near the upstream node, as the OTDR trace has less resolution and becomes noisier the further an event is from the OTDR source. Another issue is that a uni-directional OTDR is in some cases unable to distinguish between a lossy splice and a change in fiber type, as both can generate a similar drop in OTDR signal. Implementing a bi-directional OTDR, where OTDR pulses are sent from both ends of a fiber span, is known to resolve both issues. However, conventional bi-directional OTDR implementations include using an OTDR test set at one site of the fiber span to acquire an OTDR trace, movement of the OTDR test set to the other end of the fiber span to acquire another OTDR trace in the same fiber but from the opposite direction. Finally, a composite trace is assembled in software to combine the two OTDR traces. Of course, such conventional implementations do not operate in real time as well as having additional complexity and coordination requirements.